Liquid discharge from my right breast

I'm 49 years old, married with 3 childeren: 19, 24,26 (all breast fed), generally healthy. My father died of lung cancer 17 years ago. My aunt (my mother's sister) had breast cancer.
For the past 10 days I have noticed that a clear-yellow liquid is discharged spontaneously from my right brest nipple. Only once in this period I felt an itch. It passed away after a few minutes. The apper part of this nipple apears like a blister. In fact the liquid discharges from the center of this blister. The last memograph, 18 months ago, was ok.
My gyno didnot find any lumps or irregular symptoms for this discharge. I was sent to a surgen who also didnot find any unusual symptoms (visual inspection and feeling with his fingers). I was sent for a memograph test (due tomorrow).
My questions are as follows:
1. If the results of the memograph test prove that everything is ok, does this result in the conclusion that I have not got cancer?
2. If the memograph test are not conclusive then what other tests are available to negate the prsence of cancer cells.
3. What can be the cause of above mentioned liquid discharge other than cancer?

It would be most appreciated if you could answet above questions as I'm worried not knowing the cause of the liquid discharge.

[CCF-RN,MSN-rf]

Dear SDali:  1.  A mammogram is a test that can show densities in the breast tissue as well as clusters of calcifications that can be concerning.  It is not a perfect test, however, and cannot guarantee that all is okay.
2.   I am unclear as to whether this is nipple discharge or discharge coming from a blister.  If it is from the nipple, a ductoscopy or ductal lavage can be done.  If it is from a blister, then a skin biopsy can be done.  
3.  It is not unusual for nipple discharge to occur at certian times in a woman's life.  The time to be concerned is when the discharge is bloody or white and sticky, is unilateral (on one side), and is spontaneous.  Since it is one-sided and spontaneous, you have done the correct thing by seeking your doctor's attention.  If this is not nipple discharge, is there an injury?